text:
Can you fly a glider in a cloud on primary instruments?
Assume you enter a cloud with no visibility of the horizon. Your glider is not equipped with an artificial horizon, turn speed indicator or the like.
You must fly within safe limits, using air speed, ball, yarn, compass, variometer, altimeter and what basic instruments are available.
Is this possible, and how difficult is it? Can most "normally skilled" pilots do that without extensive previous training?
For example, if you just correct the yarn with the ailerons, the speed with the elevator and keep rudder neutral or fly a fixed compass heading, is that likely to keep you flying safely until you're out of the cloud?
Edit:
I now remember an old "story". I am not sure I remember it correctly though. What is certain is that in the "old days" some instruments were sometimes sealed before a competition, in order to (try to) make it impossible to go into clouds. I think it was the turn speed indicator and also the compass? But some pilots were caught cheating by bringing a small compass in their pocket.
OK, I am not sure I am telling this story correctly. (Nowadays they check GPS logs and compare to cloud base altitude.) If I remember correctly, these pilots were willing to fly in clouds and also curve using only primary instruments.

Flying in IMC for non-rated pilots, even with all the instruments available, is very dangerous and has killed many people.  I can't see why gliders would be an exception.

@Simon: This opinion is shared on this PPRuNe thread: "it rates with storm chasing and hand feeding sharks on the common sense scale".

There seems to be strong emotions and funny expressions involved. Sometimes this hides the true situation. It is not advisable, but is it likely to keep you alive (or at least not having to see your precious glider in parts while you land in a parachute). // I definitely discourage anyone from trying, I have not tried myself. But even so, I try to keep an open mind on the subject.

Why would you try to keep an open mind on something that usually kills people?  The fact that you are required to wear a parachute, even when trained, should answer your question.

I did cloud flying or "Blindflug" as passenger in a glider with my father in the 80s, who actually had a special license for that at the time (those are not issued any more). We entered a nice Cu and came out on top a few minutes later with a Blanik with a turn-and-slip indicator. Pretty cool, but: After a few seconds, you loose any orientation whatsoever. I could not even tell which way we were turning. So: No way, you need at least a turn-and-slip indicator, and then proper training to interpret and react correctly.

I've posted to ASE many times about the formerly widespread practice of flying gliders in cloud using a turn rate indicator as the only gyroscopic flight instrument. I've even done it myself a few times (but in this case the t.r.i. was actually a recently-designed peizoelectric device) w/ both sailplanes and hang gliders, and I've also done it in several light airplanes including Ces 120 w/ the vintage turn rate indicator as the only gyroscopic flight instrument. Basically, what pilots call "partial panel" flying. But, that's not at all the same as having only primary instruments.

The basic answer should be "no, normally, not safely."  But some gliders do have a fairly safe "benign spiral mode" that may save the pilot's butt if he trims the glider a certain way and takes his hands off the stick and the air is not too turbulent.  Depends on all sorts of variables like cg of glider, amount of friction in control linkages, etc.

The idea of a pilot willing to use a compass that could be carried in the pocket, not rigidly mounted to the aircraft, as the sole cloud flying aid (plus yaw string and other basic instruments) seems utterly fantastical.  Plus I highly doubt compasses (compii?) ever were "sealed" (covered), only actual gyro instruments.  Since everyone knew most compasses were pretty much useless in cloud anyway.  And you might need it to get home even in good visual conditions.  But yes, in the "old days", cloud flying relying on the turn rate indicator as the only gyro instrument was not uncommon --

With basic instruments (altimeter, speed and climb indicator and compass): Forget it!
A glider can enter a cloud when thermalling into it from below. Below the cloud the rising air was governed by dry adiabatic laws. Once it crosses into the cloud, the air is fully saturated and humidity starts to condense - after all, this is how clouds form. Now the rising air gets additional energy from condensation (its lapse rate goes down from the usual degree per 100 m of the dry adiabatic lapse rate to half a degree per 100 m) and the thermals inside the cloud become stronger. This is to say that turbulence will be more violent and the airplane will be tossed around. It will bank and pitch, and there is little chance that it will stay level for long. Since the spiral dive motion has very little damping, the glider will soon enter a spiral dive and overspeed.
The advice I got for the case that you are "sucked" into the cloud always was: Let go of the stick and open the speed brakes. Then wait until it gets light again.
In the 1930's some competition pilots tried to gain additional altitude by entering clouds. The results were catastrophic. In some cases the cover of the wings was torn to shreds by hail, and even bailing out would not be safe: One pilot froze to death when strong thermals inside the cloud lifted him to more than 8000m while he hung on his parachute.
I have done it once on a calm day when returning from the Alps. In the mountains the cloud base is higher, so it is entirely possible to arrive at the clouds over the alpine upland above their base height. I had a GPS on board that told me that I would reach the glider port safely when flying a straight line. It was late in the day, the thermals had died down and the clouds were fuzzy already, so little turbulence could be expected. One was in my way, and I went into it and flew out less than a minute later. The whole thing was completely uneventful, but I would not had done it with active thermals.

+1 But letting go of the stick and hitting the speed brakes in a cloud only works if you are high enough in altitude and not near a mountain.

@Robusto: Certainly. If the clouds touch the ground we speak of fog. I was speaking of proper cumulus clouds on a sunny day. Remember, just before you entered the cloud your sink speed was not high enough to prevent being sucked in from below.

@PeterKämpf what aircraft types do you fly?

@AlbinStigo: Gliders, Motorgliders and single engine GA aircraft.

Yes it is possible to fly in cloud in a glider. In fact there is an endorsement for it for your licence with an exam. (In the UK anyway.)
It does only require primary instruments, the one used for cloud flying is called a turn and slip, showing bank and yaw. Along with the yaw string. These are found in almost all gliders I have come across.
It is generally an endorsement only held by otherwise experienced pilots, and isn't done for prolonged periods of time. But, you are then licensed to do so.
It is easy to become disorientated, and be in odd angles of attack etc. So you must learn not to trust your feeling. I have heard of goggles used in training to cloud your vision.

This now depends on whether a turn-and-slip indicator is considered part of the standard instrumentation. In Germany, this would not be considered a "primary instrument" as stated by the OP.

The question clearly states that a "turn speed indicator" (e.g. turn rate indicator) should not be considered to be a primary instrument.

It would be difficult to stay stable for any length of time because those basic instruments give you almost no information on your angle of bank.
If you could manage to keep your spirit compass on a constant heading and keep the yarn straight, your wings would be level.
So while it would be possible, I would think you would need an experienced glider pilot and relatively calm conditions to maintain wings level for any usable length of time.
It would be interesting to hear from someone who has actually done it.

"none of those basic instruments give you any information on your angle of bank" / If yarn is straight and compass heading fixed, wings are level

Good point. I hadn't thought of that. I think I will need to edit my answer.

Although @ycc_swe is right up to a point, I would not include that in your answer. Those instruments don't give a pilot enough information to correct problems.

Why would it be so different to read the compass instead of the turn-speed-indicator? We are not discussing precision here, just flying within safe limits. Mostly flying straight forward or making slow turns. / I am absolutely not advising anyone to try. I haven't tried myself. We are discussing if you can save your life/glider in an emergency, even if it naturally is better and very possible never to enter a cloud under these premises.

@ycc_swe The magnetic compass isn't that steady an instrument.  I can't imagine a pilot being able to prevent a spiral dive using only the magnetic compass and yaw string.  Even with a gyro compass, that seems like a tall order.

@WayneConrad: Isn't that the sort of thing gyrocompasses are for?

@Sean Not normally, as far as I know.  Maintaining attitude in IMC is normally done with an artificial horizon, or if that fails, a combination of turn/bank indicator and ASI.  The gyrocompass is used for maintaining heading, of course.  But I don't know how many gliders have any gyro instruments at all.  Things might have changed, but they used to be kind of power hungry instruments, and gliders didn't used to have much of an electrical system.

@MikeSowsun -- re "If you could manage to keep your spirit compass on a constant heading and keep the yarn straight, your wings would be level." -- I have done exactly that in a Cessna 120 in stratus cloud.  Actually I didn't worry about the slip-skid ball (gives same info as yaw string), in fact I used the rudder not the yoke for steering, so the ball was often a bit off center.  Key was to choose a heading with a large southerly component, so compass errors worked for me (made compass extra-sensitive to bank) rather than against me (giving a wrong-way indication as started to bank).

But, due to the necessity of maintaining a southerly course, this technique would not have allowed thermalling.  Continuing on the same theme, once I flew a hang glider up into a cloud using a primitive home-made turn rate indicator (piezoelectric, no moving parts), which worked ok, but when it came time to hold a straight-line course to exit the cloud (because my glasses were starting to ice up) I found that my magnetic compass was actually more useful than my turn rate indicator or my GPS-based heading indicator (GPS-based heading isn't useful when groundspeed is near zero).

But would never dare try this intentionally in thermic turbulent air without some sort of actual turn rate indicator to fall back on in the case of accidentally entering the beginning of a spiral dive-- compass will be useless in such an event.

I'm offering this answer more for amusement to readers than anything;
everything is factual first-person observation by me.
No.  I cannot fly a glider in a cloud on primary instruments.
When I was a young man of 23 years old I flew hang gliders before I obtained my Private Pilot's license in the USA about 1986. My flight instruments in my hang glider were an aircraft altimeter with 20 foot resolution, a variometer that was sensitive to about 50 foot per minute climb/descent rate, and very sensitive airspeed indication by human ear.  I lacked any turn or bank or artificial horizon.
In my flying club it was common knowledge that intentionally flying into a cloud like a cumulonimbus was tantamount to suicide.  This was about 1986 and already there were a number of reports of hang-glider's deaths from hypoxia and hypothermia from thermallinig up into cumulonimbus clouds.
Once in a competition flying from Crested Butte Colorado USA I was in such a strong thermal that it took me over one minute to exit a thermal and I luckily did exit it at 17000 feet MSL.  Imagine this; usually glider pilots seek lift.  In this case I identified it was dangerous and dove a straight line to exit the thermal and just escaped zero visibility within the cloud deck of 17000 feet MSL.
My total flight time that day was 4 hours and 20 minutes with a maximum altitude of 17,000 feet above sea level.
In my years in the flying club I knew of one individual that fought  being lifted into a cumulonimbus cloud by performing wing-over maneuvers which is an easy way to waste energy meaning to waste altitude.  He eventually broke the spar of his hang-glider with excessive G forces, then spiraled like a maple seed under his busted glider and saved himself at lower altitudes with his emergency parachute.  He's the only hang-glider friend I know to have deployed a parachute.
I hope this was fun to read.  Comments or questions are welcome.

thanks for sharing- -see my related comments under this answer https://aviation.stackexchange.com/a/26809/34686

I was taught to fly in cloud using basic instruments in 1976.  The problem was one of staying in the cloud without exiting through the side. In the event of losing control, the drill was to open the air brakes and wallow out of the bottom.  This worked well enough in my Olly 2B until one day in 1978 it didn't. My cosmim indicated a maximum climb rate and my altimeter needle moved round the dial at an alarming rate. I had entered cloud over Parham with a light northerly breeze drifting me south. With my air speed overtaking maximum rough air speed I decided to raise my nose and deploy air brakes. I have no idea how long I remained in cloud but when I finally escaped the murk it was near the top, very high and out over the channel. I never flew in cloud again.

"cosmim"?  What is that?

Cobb-Slater Variometer.  See https://baec.tripod.com/JUNE98/gas.htm

In some gliders "the cloud procedure" is you trim it at around 1.3*Vstall and let go of the controls with air brakes wide open. It spirals down in a controlled fashion and then you hope to exit the cloud and take the yoke back. I used this to get down twice in waves when the hole closed up, every time the decent took longer than I thought with eyes fixed on the altimeter :)
Someone may argue that hands-off the controls is not considered IMC flying, but it's definitely better than trying something fancy. Gliders have a tendency to over-speed beyond their VNE as they have less drag, so keep your hand on air brakes during cloud entry!
Some gliders are not certified for cloud flying due to their instability in spiral dives, you can check this while in visual conditions or refer to the POH.
PS: in the UK it is legal to fly glider in IMC in class G airspace as long as the glider has a turn indicator and the pilot has a cloud rating. Mine did not have any useful IFR instruments when it happened but I did complete glider cloud training.

Is there really a strict correlation between the glider being unstable in a true hands-off spiral, and the glider not being certifiable for cloud flying?  What if at least one (turn rate indicator) gyro instrument is installed?  I would think that many gliders would be reasonably controllable in cloud in that circumstance, even if slightly spirally unstable hands-off.

I've done it many times to climb slightly into the cloud (in situations when the risk to meet with another fellow in the cloud is low, i.e. far from any airfield and there are quite lot of useful clouds nearby). Immediately after losing visual to the ground I level wings and quickly find my way out of the cloud. Punching a hole on the side of the cloud and scooting into sunlight with 200km/h is something what I really like in flying gliders :) But this is not real IMC flight just biting a bit into the cloud. I once tried that how long I can maintain spiraling in a cloud just by pants (so w/o turn indicator). And even a slight turbulence was enough to confuse my senses, so I opened speedbreak and left the cloud. What surprised me was that I entered into cloud in a left spiral and descended out of it in a right spiral - without even noticing this direction change. Important fact that I done this experiment in a glider which has speedbrake effective enough the keep the speed below Vne even in vertical dive (fortunately I didn't have to use this capability in this situation). So I'd guess that even with significant IR experience it is very difficult if not impossible to maintain a steady spiral in a cloud without proper instrumentation (like a turn indicator).

Thanks for sharing an interesting experience. I hope you really consider safety aspects. // If I "got caught in a cloud with only primary instruments" I would control elevator after airspeed, ailerons after yarn and keep rudder neutral (or fix a compass heading). My guess is I would survive (unless extreme turbulence). Could I save myself a parachute jump that way?

It's extremely dangerous to do this @hunglider, you are taking a big risk every time you go into cloud. One of the big lessons in IR training is that you cannot trust your senses - your inner ear is easily fooled.

ycc_swe: w/o turn indicator you are short of information. The whiskey compass is not for determining the turn rate. In an unsteady condition it will just tumble w/o providing any useful information. If things went out of control, relying on the inherent bank stability of the plane could be much better than try to control based on false info. So the second best strategy in case you sucked into a cloud accidentally is to open speedbrake and release everything. The best strategy is not to caught in IMC accidentally especially if you are not trained for IR or don't have proper instrumentation.

@hungglider Yes, using brakes must be right, unless very low clouds/fog. I don't think that will worsen anything. // Inherent bank stability is a very important factor. // Regarding the Edit I made in the question. I am not sure I remember correctly but I wonder if the oldtimers curved in clouds with only a compass they brought in their pocket :) "Just radio the other guys, they must wait 2 min before the next guy goes into the same cloud" ;)

And pitch I think you should definitely control reading air speed. Maybe just using trim.

The VMC criteria define legally whether you have the choice to fly VFR (in the UK and Europe).
In the UK, you can only fly either VFR or IFR*.
If you are flying close to (or within) a cloud, you must be flying in IMC which logically means you must be flying IFR because the VMC criteria cannot be met.
The fact you have a cloud flying endorsement / IMC rating means you must be flying IFR whenever you are less than the legal VMC.
If I'm wrong, please let me know how, I've been trying to reconcile this in my head for ages.
*Excluding Special VFR, and excluding clear of cloud in sight of surface at or below 3000ft, not relevant here.

I have heard from high hour wave pilots where the clouds close in beneath them before noticing (or enough time to get back down to the holes) that if they just point the glider away from the mountain, level their wings, begin their descent, then just hold that position as they enter the cloud by keeping the compass fixed, yarn straight and airspeed constant their glider will live for another day (assuming far enough away from heavy rotor). In theory the same should work if one is sucked up into a cloud. Not legal.

Yes, wave clouds have nice, steady airflow. Most clouds a glider pilot will encounter, however, are cumulus clouds with a high level of turbulence inside. That makes a big difference!

In my experience, in the northern hemisphere, this only works well on southerly headings, even if the air is rather smooth.  Has to do with the effects of lead / lag errors.  Have video of a ces 120 descending through several thousand feet of cloud using wet compass for heading, w/ turn rate indicator covered up and no other gyro instruments present --  on a southerly heading.  Also an experience in hang glider where wet compass outperformed gps as an aid to holding heading to exit cloud, with additional help from piezoelectric turn rate indicator -- but only on a southerly heading.

As a student I flew in a cloud in a Blanik with my instructor flying, we entered the base of a cumulus at about 1000 m and left at 2100. He was using only a turn an bank indicator (or turn and slip), mine was inoperative because it had no battery.
This part of the flight was uneventful.

I've posted to ASE many times about the formerly widespread practice of flying gliders in cloud using a turn rate indicator as the only gyroscopic flight instrument.  I've even done it myself a few times (but in this case the t.r.i. was actually a recently-designed peizoelectric device) w/ both sailplanes and hang gliders, and I've also done it in several light airplanes including Ces 120 w/ the vintage turn rate indicator as the only gyroscopic flight instrument.  Basically, what pilots call "partial panel" flying.  But, that's not at all the same as having only primary instruments.

The question clearly states that a "turn speed indicator" (e.g. turn rate indicator) should not be considered to be a primary instrument.  So, long and short, I'm afraid your story, while interesting, doesn't really answer the question that was actually asked--

PS-- which part of the flight was eventful?

(Upvoting anyway just for the heck of it; love to hear stories about gliders flying in clouds)

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review


text:
Why retract flaps at go-around?
As I understand the procedure for go-around it includes retracting the flaps.
Why is this?
The decision to make a go-around must sometimes be made quickly, under stressful conditions, like in bad weather. Retracting flaps introduces one more thing to do under sometimes stressful conditions.
Speed is low during landing and by retracting flaps you give away safety margin for lift. (Speed may also slow further since the nose is raised during go-around.)
Retracting flaps may also affect pitch and thereby make control of the aircraft slightly more difficult in a situation which may already be stressful.

may be it is to reduce the drag?

I would think that drag is less important to consider in that situation, compared to the risks I describe in the question. / But I am a glider pilot, we do not make go-arounds, so I don't know.

Related but with somewhat opposing answers

@TomMcW The other answers aren't really opposing. They just say you shouldn't adjust configuration immediately when the go-around is called, which is still true. Wait for terrain clearance first, then start fiddling with configuration (making sure you have enough airspeed for each adjustment before you make it.)

@reirab I see, the other question is more about the timing of config changes. Makes sense. Retract to soon you risk a stall. Retract too late you might not climb quick enough. Sounds like it might be a little tricky if you have tall trees ahead

For the same reason that you don't takeoff with full flaps. Because the climb performance sucks.
Flaps do add lift, but also a lot of drag. A low flap setting often provides more lift than drag, assisting climbout, whereas full flap offers a whole lot of drag, which is desirable when you want to be slow for landing.
But a go-around necessitates gaining height quickly, which will not work with landing flap selected. The usual procedure, at least in light aircraft, is to wait until the vertical speed is neutral or positive before retracting flap. This minimises some of the risks you've raised about aircraft control.
It is often said that a go-around is a period of heavy workload, and managing the flaps and airspeed is not easy. That is why the go-around is a fundamental procedure taught right from the very beginning, and practiced and tested regularly.

Pretty much - I suspect most students have attempted a go around with full flaps. The twice I've done it my immediate thoughts have been "Why the hell aren't we climbing?"

its also very important to retract landing flaps in a missed approach

What Ben said. Also, when adding full power on a go-around, some planes pitch nose up or down with full flaps.

I was once doing a soft field takeoff and inadvertently fully extended the flaps rather than fully retracting them. I popped up 50 feet in the air and then suddenly found myself slowly descending, unable to climb, and on the verge of a stall.

"Because the climb performance sucks."  Straight to the answer.  I like your style.

So then what do you do if you need to go around but the flaps won't retract?  That seems like a pretty major certification oversight.

@Sean fear not - certification requirements include a minimum climb gradient that must be achieved in the landing configuration, so even if the flaps and landing gear are somehow both stuck down the thing can still climb. It just won't climb anywhere near as fast as desired.

You correctly point out some of the challenges surrounding the procedure of retracting flaps upon go-around. Go arounds can be a stressful situation, flaps do give additional lift and margin against a stall, and retracting them does result in a pitch change for which the pilot must compensate. Allow me to address each of these concerns in turn.

A go-around can be a stressful situation—especially, as you point out, if additional concerns such as weather come into play. Outside of the training environment, a go around is usually executed because some aspect of the landing is not right, whether that be the pilot, the airplane, the weather, the runway, other traffic, or any combination of those or numerous other conditions. All of these can add up to create a very demanding situation indeed. For this reason, the go-around procedure is carefully taught and practiced often in primary training, and pilots continue to practice and demonstrate it throughout their career. Now, raising the flaps is a normal configuration change that experienced pilots are used to making. Even in demanding situations, raising the flaps should not make an excessive demand on the pilot's attention. This includes already demanding situations such as during a go-around.
Airspeed is a major consideration during go-around. Flaps do give additional margin above the stall, some designs more than others. A go-around is all about transitioning from the low-speed approach to the generally higher speed climb out. Thus, the aircraft will be accelerated, typically to the best rate of climb speed (Vy). Typical go-around procedure will call for retracting the flaps once the aircraft is stabilized with sufficient speed, thus reducing—if not eliminating—the risk associated with reduced margin above stall. Even then, the flaps should typically be retracted slowly and in stages, allowing for the speed to increase appropriately. Putting all this together, proper flap retraction during a go-around will not result in excessive risk exposure due to airspeed consideration.
Retracting the flaps does result in a pitch change, though different types of flap designs will result in different amounts of change at different rates. Again, the pilot should be experienced and practiced in compensating for this change. Again, since the flaps will typically be retracted slowly and/or in stages, the pilot will be able to compensate throughout the retraction process. During the go-around, the pilot is already making numerous pitch changes and compensations as power, airspeed, and lift change; compensating for flap induced pitch change is part of the expected process.

Now, your question was why should we retract the flaps during a go-around. I have addressed your valid concerns above. Now allow me to give a some reasons why retracting the flaps is advisable or necessary.

Flaps reduce climb rate. Flaps add drag which is a good thing for landing, but not good for the climb. In retracting the flaps, the aircraft is configured for its best possible climb performance. Some aircraft have such limited performance that they simply will not climb with full flaps, even at typical elevations and in typical weather. At high elevations and in hot weather, most aircraft will have substantially diminished ability to climb with full flaps.
Each type of aircraft has a speed limit for how fast the aircraft is allowed to go with flaps extended (Vfe). This is for structural considerations so that the flaps and wings are not damaged by excessive speed. Retracting the flaps allows for acceleration to climb speed and above without the risk of overspeed damage to the flaps. It is very possible, in some aircraft, to overspeed the flaps after the go-around if they are not retracted soon enough.
For multi-engine aircraft, having the flaps retracted typically puts the aircraft in the best configuration to handle an engine failure emergency. If one of the engines fail, the aircraft will climb best on the power of the remaining engine(s) with the flaps retracted.

Since the first objective of any go-around is to establish a stable climb-out, the procedures involved all revolve around changing the current configuration to the required climb-out configuration. Stuff like power-up is pretty obvious in powered aircraft, and since most aircraft use far more flaps for landing configuration then take off, selecting take-off flaps also begins to seem more obvious.
The original question is based on an incomplete understanding about how flaps work, which some of the other answers here have not helped clarify. Most people know that flaps affect lift, drag and attitude, but tend to forget that each is affected by airspeed at different rates. In particular, drag increases far faster then lift when airspeed increases and this is why most aircraft use far more flaps for landing then for take-off. Also people tend to often forget that flaps are used during take-off to reduce the runway requirements, not to increase climb rate, and in a go-around, you are not on the runway so it is not a factor.

Retracting flaps on a go around is not done until a positive climb rate is attained. And even then it should be done incrementally as airspeed picks up. The specific checklist varies among planes, but generally speaking you throttle up, remove carb heat, attain a positive climb rate, (raise landing gear if it is retractable), remove one click of flaps, wait for speed to increase, remove more flaps, wait for speed increase, rinse and repeat...
A go around isn't unlike a takeoff, you want to be climbing as fast as possible, shedding the drag caused by the flaps allows you to pick up speed faster, resulting in a safer climb. But, you can't just fully retract the flaps immediately because they are providing significant lift, you could slam into the ground if you aren't climbing or if you reduce flaps too quickly. There is also the danger of stalling if you reduce flaps before your speed has picked up sufficiently.

Flap retraction is not always accomplished after positive rate. Some situations, such as wheels already on the ground, may call for initial retraction with no climb rate. This will depend on the situation, the aircraft, and pilot judgement.

First of all, if you fly faster than a stipulated speed with flaps deployed it can damage the flaps, so just in the interest of getting the airspeed up alone, you usually need to retract the flaps as soon as possible.
Flaps are kind of like brakes, they slow the plane down. Not a good thing when you are trying to get to altitude.

Flaps change the wing properties and thereby changes the lift, the approach attitude and lowers the stall speed (all landings are basically controlled stalls). If you need to get out of trouble quickly in a go-around then you may need all the energy that you can get, retracting the flaps changes the wing back to the efficiency of take off to allow you to climb out of trouble.

Flaps add lift and drag. This answer is misleading.

I accept. Do you suggest I delete ?

Usually you want to [edit] to fix any issues with a post that are raised in the comments. If the issues aren't fixable without completely overhauling the post, sometimes deleting and possibly starting over is the better thing to do, especially if the issues are serious (saves you from the risk of receiving further downvotes while you are fixing the post). Note that having a large number of downvoted and/or deleted posts may restrict your ability to post further. You can delete, edit and then undelete if you want to.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What is the correct IATA airplane designator for the Boeing 787-10?
Wikipedia claims 781, most other sources say 78J.  I can't find anything authoritative, and IATA has the gall to want US$578 for the answer.  Which one is it?
Update for clarity: Everybody agrees that the four-letter ICAO code is B78X. I'm interested in the three-letter IATA code.

IATA isn't ICAO. The title and question body says IATA, but the WIkipedia link says ICAO, and it would seem that ICAO is what you're going for. Please [Edit] appropriately.

@aCVn The Wikipedia page actually lists both ICAO and IATA (2nd column) codes. It does indeed say B78X (ICAO) and 781 (IATA) for the Boeing 787-10. The references on the Wikipedia page only list ICAO codes though...

IATA must make literally thousands of dollars annually from this charge.

Until yesterday we had an answer from someone who actually asked IATA and posted their reply. What happened to that answer?

@PerlDuck I've just accepted that answer.  There was a third answer offering dubious sources, but that was heavily downvoted and seems to have been deleted now.

@jpatokal I meant another one. It was posted yesterday by someone with (I guess) ~7000 rep and is now deleted. Last time I looked it had +3. Never mind. Maybe I ask someone in the chat.

I still do not consider this question satisfactorily answered, and I think @jpatokal you may very well have awarded the bounty in vain. I'm not calling anybody a liar, but there's just no way to verify the contents of IATA SSIM Annex A (the correct product number of the current SSIM Appendix A would be 8803-28). The deleted answer referred to above was downright weird, as it claimed to show a direct quote from an email, but the embedded link in it clearly was not from an email created by IATA SSIM Team, as it referred to ESA site. That just does not happen with copy/paste

@ymb1 ok, that would explain it, but I still think it's odd. Not saying I would not be able to make a mistake like that myself...  I do understand very well that rep can measure trust, especially when it's in thousands, hard to get there dishonestly.

I looked it up in the corresponding IATA document and I can confirm it is 781.
Sadly I think I am not allowed to attach any kind of proof from the document but the source of my information is IATA document 8803 - Aicraft Types in version no. 28.

United flies the 787-10 between Newark (EWR) and Frankfurt (FRA) on the 787-10. Knowing this, I did a search on ITA with an extension code to filter for specific aircraft types in the results. With either AIRCRAFT t:787 or t:781, the expected flight was returned. Using t:78J with the rest of the search unchanged yielded no results, so it appears that 781 is at least valid, and possibly the definitive answer since it seems unlikely that multiple codes would be in use.

Note: Wikipedia has now changed to 78J. The change was done on 1 June with the reason: "Wikipedia is the only source on the internet that claims 781".

This answer unfortunately does not provide certainty into this matter. Yes, 781 would appear to be a valid code for 787-10, but there is no proof it is the official IATA designator.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How can I determine takeoff and landing from an ADS-B feed?
An ADS-B feed consists of a series of latitude, longitude and altitude points, without any "start" or "end" markings as such.
Using this data, which can contain arbitrary gaps and errors, what's the most reliable way to determine when an aircraft has landed or taken off at an airport?
Update: I'm looking at preprocessed feeds in VRS's AircraftList format, which on closer inspection has a boolean "Gnd" field.  (Note that there's no guarantee that any but the most basic data fields will actually be available in practice.)

I would use when the altitude is +/- 100 feet of the field elevation and its speed has dropped below 40 knots. You could use ellipsoid height if you want to make it simpler but you'll probably have some issues in high altitude areas.

It depends on the type of ADS-B feed you have.
On the lowest level, the messages transmitted from the aircraft, usually contain information about the air/ground status of the aircraft1. When the aircraft is airborne, Airborne Position Message are transmitted (types 9 - 18 or 20 - 22) for position and altitude. Airborne velocity is in message type 19. On the surface, message types 5-8 are used to transmit both surface position and movement. So by looking at the raw messages, the transition between airborne and surface type indicates landing, vice versa in indicates take-off.
This is accurate for most larger aircraft, smaller aircraft and helicopters don't always have a weight-on-wheel switch or similar device that is used to toggle the air/ground status. In these case speed may be used as trigger which is a less accurate indicator.
If you don't have access to the raw messages, you have to find an other way to do it.
Typically ADS-B feeds for air traffic control consist of ASTERIX 021 reports. If you have an ASTERIX category 021 data stream, the air/ground status of the aircraft is included in Item I021/040, first extend, bit 7 - Ground Bit Setting (GBS).
If you have a stream with only latitude, longitude and altitude, then I would try to use the altitude field. On the surface there is no altitude transmitted (it is not in message type 5-8, the bits are used for surface movement), so if the altitude is no longer there, you can expect the aircraft to be on the ground. However, this depends of course on the implementation of the ADS-B decoder; it may just give stale altitude data instead of blanking the altitude on the ground.
If you don't have good detection near the landing zone, you can try to extrapolate the altitude graph from the final approach section and based on that estimate when / where the landing would be. You may want to adjust for the flare if you need to.

1I am assuming 1090ES ADS-B here which is the defacto global standard; UAT and VDLm4 technology varieties of ADS-B also contain air/ground status but in a different manner.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Were there any test flying incidents during which the pilots managed to escape the plane?
I am only asking about flight testing civilian jets, not military ones. I know that all test pilots have to be equipped with a parachute, so I wonder was there any incident where the test pilots and test engineers had to leave the plane during the flight, and managed to reach the earth? Alive or dead.

Escaping with a parachute is always difficult, and specially difficult in fast airplanes, like jets, without the help of an ejection seat. It is, however, not impossible (the exceptional case of Gary Powers and the U-2 is a good example) but it's rare...

Is the OP asking for bailouts only?  If no: I remember reading in "Yeager", the autobiography of Chuck Yeager, about 2 situations while he was a test pilot at Muroc AFB: the first was a training flight in an F-104 with 2 test pilots where the engine went out on takeoff and one pilot ejected, the other stayed (turns out if the second ejected he would have died, and if the first stayed he would have died), both surviving; the latter is Yeager's ejection from an NF-104 while commandant of ARPS (http://www.kalimera.org/nf104/stories/stories_12.html).  Don't know of a database for these though.

Whether inside the plane or outside, dead or alive, the crew all manage to reach the earth after each and every test flight. Gravity can be cruel that way.

Do civilian space ships count?
In the VSS Enterprise crash  the captain survived. The plane broke up around him and he was able to unstrap his seat after which his parachute automatically deployed. The co-pilot died in the crash.

You can see a bit more details about the accident and how the pilot got out on this video.

Yes.  Here is a (long) video of a test pilot spinning a Bonanza with a cockpit POV.  He ends up bailing out.  Skip to 11:30 to watch the entry.
Ovbiously not a jet, but maybe it's close to what you're looking for.

I think you need to skip to 12:30?

YouTube something like "bonanza spin" or similar.  The video is widely available.

During the early development flight tests of the Challenger, an aircraft was trapped in a deep stall. Two crew members bailed out, but the final crew member did not survive the bail out.
http://www.check-six.com/Crash_Sites/Canadair-CGCGRX.htm

In the remote-controlled crash of a 727, https://en.wikipedia.org/wiki/2012_Boeing_727_crash_experiment, the crew (and some camera-men) left by parachute...


text:
What is A320 "PC DEDICATED TO MAINTENANCE"?
What is meant by "PC DEDICATED TO MAINTENANCE" in the FCOM of A320 in cockpit preparation?
I could not understand what is meant by this item.

more context is needed.

This is very airline specific. If you are a online pilot, it doesnt apply to you. If you are about to join an airline, they will tell you. Just know it is there.

At least one airline's SOPs (although for an A340) clarify that this means:

Check that the Personal Computer (PC), dedicated to maintenance use and located in front of the 4th
occupant console, is stowed.

The A320 manual from Airbus has the following content:

Check that the Personal Computer (PC) dedicated to maintenance use and located in front of lower stowage at RH rear corner is stowed.
Check that the light of its manual switch is off. If not, switch it off.
Check that its associated printer located in front of RH rear of the cockpit is stowed.


text:
Was the "Air Berlin" lap of honor over Düsseldorf problematic?
A few days ago, flight AB 7001 (Air Berlin, New York - Düsseldorf) went for a "lap of honor" around the airport.
One video can be found here.
No emergency or technical issue, it just was that airlines last ever flight on that route (they're bankrupt), and the pilot wanted to give a nice gooodbye.
Now, of course comment-sections on news regarding this are full of "experts" saying if it was ok or not. Here the question for the ACTUAL experts I can reach:
Did the pilot do anything "bad" or even dangerous, or should a quick circling of the airport be just fine as long as the pilot can actually, well, fly his airplane properly?
UPDATE:
The Bundesaufsichtsamt für Flugsicherung (BAF) (German bureau for flight-safety) agrees with this page, the manoeuvre was ruled to have been legal and safe.

As far as I know airplanes are not allowed to just fly randomly, especially over an airport: position, direction, speed, altitude, they are mostly dictated by the tower. The only safe way to say if it was dangerous or not is to know if it was agreed or not with traffic control; the currently accepted answer is not an answer at all (just an uninformed opinion) and anyway you are supposed to wait a bit before accepting an answer, to give other people time and interest to reply.

Wich proves I am clueless about flight-rules... Airplanes fly, towers mostly tell them where to. Thanks for the heads-up about this being no "flight-control-legal" (???) answer. I need some terminology for aviation-discussions, really , I feel like randomly stumbling through a dictionary here!

@motoDrizzt your comment confused me when I read "the currently accepted answer" because I don't see any accept mark unless it's the most upvoted answer (or the only answer) at the time you wrote that comment

@Andrew T.: An OP can retract an accept mark. I assume that’s what happened here.

The tower was upset because he spilled his coffee.

Apparently the tower ATCOs were fully aware of what was going to happen, cameras were on, and everyone looking for the show. When the "Good Luck Bokke" flight happened over Ellis Park in '95, news also said the crew went mad, doing dangerous maneuvers, while the truth is it was carefully prepared with ATC over the past week, the aircraft had no passengers, and the Chief pilot of the airline was in command. And it was reiterated in 2013.

The maneuver was safe.
A spokesperson of the DFS (German Air Traffic Control) told the Berliner Morgenpost that the pilot requested and was given clearance to fly a left curve in case of a go-around. The necessary distance to other aircraft was ensured and a specific height for the maneuver was not determined.
The spokesperson also said that the DFS believes that this maneuver was safe.
However the LBA (Federal Aviation Office) started examining the case and requested Air Berlin to submit a statement which provides a reason for the go-around. The editorial staff of that newspaper believes this to be a routine procedure.
source (in German)
A rough translation of the relevant part in english:

Christian Hoppe, spokesperson of the German Air Traffic Control confirmed that: "The pilot previously requested if he is allowed to fly a left-curve in case of a go-around and was given clearance." The necessary distance to other aircraft was ensured, the specific height of the maneuver was not determined. "From the DSF's point of view the maneuver was safe." The Federal Office for Air Navigation corrected earlier information, which claimed that the pilot had reported problems with the landing-gear. "That was our assumption."
The Federal Aviation Office will nonetheless examine the case, Air Berlin should submit a statement on the reason of the go-around. Our editorial staff believes, after multiple requests, that this is most likely routine operation.

another source to add; it appears the pilot is now suspended by the airline.

Thanks! Between the "real" reports, those trying to be sensational and those just badly researched and/or speculative, it's hard to filter out the useful one! But this one DOES look good and sensible :).

@Bageletas Since it was already the last flight ever of that airline, I wonder what they try to accomplish with that.

@Mast: the captain of the flight announced to the passengers, that this was the last long distance flight of Air Berlin and said good bye to the passengers.

@DohnJoe Not the pilot, but the airline grounding the pilot. Although if this was indeed the last long distance flight and not the last flight, that would explain a couple of things.

@Bageletas: Presumably the pilot could be suspended for many reasons short of an actual safety breach.  On the one hand, unnecessary use of fuel and time (both expensive resources).  On the other, even if completely safe, the maneuver was certainly perceived as unsafe by some observers (and perhaps passengers), which naturally the airline doesn’t want.

Apparently (according to news media) the crew announced to passengers beforehand that they were going to perform a low approach, fly along the runway at 200ft and then continue into the left turn. This proves that not only a go-around with the left turn was agreed beforehand, but the low approach manoeuvre (flying level along the runway which is non-standard and quite different from a go-around), too.

@Mast It was the last trans-Atlantic flight of the airline, not their last flight overall. That said, it's quite likely that the pilots in question weren't scheduled to fly again anyway and the airline's final flight is also coming up very soon (next Wednesday, Oct 25.)

It looks to me to be a simple "go-around" - a maneuver the pilots would be expected to execute if the runway were to become unavailable shortly before landing.
This can happen if the previous jet to land failed to exit the runway in time.
Some might call this bad because it delays the landing, it burns extra fuel, and it might conceivably interrupt traffic flow (are there other aircraft behind this one waiting to land?)
I choose to believe that the pilot was well aware of traffic, fuel requirements, etc. and did a good job in a safe manner.
Another thing to consider - even if the airline isn't flying any more, it's very likely that the pilots will.  Doing something dramatic and unsafe makes it very difficult to continue in their career.

It wasn't just the go-around that made this incident notable. It was the sudden left turn and flying over the terminal itself. Definitely not the published missed approach procedure!

DV and I don't get the 10 upvotes: "I choose to believe" is not an answer, just personal (uninformed) speculation.

@reirab - Agreed.  I assume the pilot cancelled IFR then called a go-around when on short final.  At that point, it's just a left turn back to downwind just as if it were a Cessna.  It's too bad we don't have the radio calls to confirm.

It wasn’t a normal go-around. It was a prolonged level flight with gear down, followed by a shallow left turn with only marginal climbing. Gear was left down very long, too. As such, it was much closer to what’s dubbed a „low approach“ than a standard go-around. This probably still was a manoeuvre pre-agreed with air traffic control, pre-briefed and, as such, most probably safe, but it was definitely not something routinely observed in normal operation.

Since the Air Berlin flight got clearance from controllers before performing this maneuver, it should be legal. The only legality is whether the flight declared a missed approach only to justify the pass. If so, the now defunct airline and it's now unemployed pilot might have some questions to answer.
There is a sad story about the last Pan Am flight. Upon arriving at Miami, being the last Pan Am aircraft still flying, the controllers actually requested that the plane make a slow pass over the field before landing, to honor the passing of a landmark airline.

FWIW, some professional pilots look askance at this particular event due to there being passengers on board ... and others see nothing wrong with it.  I've been tracking the commentary on Air Berlin's demise, to include this event at PPRuNe and see that opinion is divided.


text:
Why is "Affirm / Negative" used instead of "Yes / No"?
Does anyone know why we use Affirm and Negative in RT, rather than Yes and No? I assume it's to prevent confusion with accents and other languages - but Yes and No sound very different to me!

Welcome to Aviation.SE and with a good, original on topic first question!

Welcome! One question, one gold badge. Just go on!

Because it makes you sound cool and very Top Gun!

Negative Ghostrider. The pattern is full

Seriously though, short words, especially at the end and beginning of transmissions are often clipped. When everything is busy, a question might only need a "yes/no" reply. Yes/no is easily lost in radio communication. Affirm/negative are not.
Also, with English native speakers, yes and no are absolute.  In some languages, yes and no are relative to the question.
Interpret this:

Don't you have enough fuel to make the field?
Yes, we don't.

or

No, we don't.

Of course, the question is not good as it contains a negative but, if a question can only have an "affirmative or negative" response, it also helps the questioner to form a good question:

Can you make the field?

This can only be "affirmative (always shortened to "affirm" to avoid confusion) or "negative".  There is no interpretation.

I don't understand the point of your "Don't you have enough fuel to make the field?" example. As you say, it's a bad question to ask since it can't sensibly be answered with either yes or no, regardless of what words you use to communicate the ideas of "yes" and "no".

@DavidRicherby Yes, it's not a good example is it? I'll try to conjure up a better one, although I'm not creative at that sort of thing. I was trying to get across the point, missed by many Western native English speakers that yes and no are not always absolute. In many cultures, they are relative and yes/no answers are often misinterpreted.

French still has three words: si is for a positive response to a negative question. Middle English had four words. The Celtic languages have no words at all for yes & no: instead, you respond with a form of the verb. So yes, it's complex.

Perhaps as an example: You can't make it to the field? (Or ANY negative question, really.) With, for example, a German background this IS tricky, because German would allow both no for "no, you are wrong, we CAN make it" and "No, we indeed can't make it". Not sure how conventions for this work for a native English speaker.

@DavidRicherby It's a good example of a bad sentence.  As an answer to the question "You cannot make it?", "yes" can mean "on the contrary, we can make it", whereas "affirmative" means "what you said is correct; we cannot make it".

+1 for clipping - I remember back in the days of my Nextel phone with PTT, there were always people who'd push the button and begin speaking without waiting for the "chirp". Usually you knew what you missed from hearing the last 98% of their transmission but on a very short one like "yes" or "no" they'd actually be completely done vocalizing before the handset even began to transmit audio.

I very much like that edit Simon. Note that ICAO specifies 'Affirm' vs 'Negative'. However, the FAA deviates from the international standard by specifying 'Affirmative' vs 'Negative'.  The latter can be confused easier in garbled radio communications. I appreciate your answer is now aligned with the international convention. +1

Could also add that in some African countries, it's common to first acknowledge that you understood the question with a "yes", and then answer it (with another "yes" or "no") - a habit they may also use when speaking English.

@Layna that is exactly the point. It's just as confusing in English. Try this one, "Please turn down the air conditioning". Does that mean you want me to turn down the temperature (making it colder in the room), or that you want me to turn down the effectiveness (making it warmer)? It's a commonly made request in the US that always leads to confusion and the request for clarification.

Why do we say "TANGO" on the radio for the letter "T"? Because "T" could get garbled or misunderstood to be "B", "E", "or "V". "NO" could become "oh?", "YES" could become "us", and so on...the possible interpretations and permutations of short, monosyllabic words are many. Use a big word and it will be hard to confuse with others...

From an information-theory standpoint, the extra syllables (such as "niner" vs. "nine" that can sound a lot like "five" over a noisy connection) are "parity".  They do not add any information, but provide confirmation that the information has been received correctly.  The TCP packet used to upload this comment to SE includes a checksum that fulfills a similar purpose.  The web server's networking stack re-calculates the checksum and confirms it matches.

The term isn't so much "Parity" as "hamming distance" - the point is to ensure that there's always enough 'distance' between each transmitted symbol, that you can always detect a transmission error. That's why you get 'papa', 'charlie' instead of 'pee' 'cee'.

@MontyHarder There is also the zero-hamming distance of "nine" to German "Nein" (no) that should be avoided in an international context.

The 9 vs nein is an important one. Similarly 9 and "no" in English are still quite similar, as is "mine".

"Affirmative" and "Negative" come from the radio procedure words that went into the aviation world. As a comment above it also adds on more complexity and length to the statement so that the receiver can understand even if the transmission got garbled up or cut off in some parts. It would be really bad if the "yes" or "no" got cut off somehow from the transmission which would be really easy because they take a really short time to say, making it easy to loose the entire word over radio.

I have this argument over server names at almost every job I go to. After someone accidentally shuts down the wrong server because of this, they start to pay attention.

The use of the word "Affirmative" instead of "Affirm" seems to defeat the purpose you describe. Go guess what "crk...crk.. ative!" means.

@DmitryGrigoryev As opposed to just "crk...crk.." if they said "Affirm"?

It has to do with how radios in general work or worked. This is also true with telephones and some VOIP situations.
So take a plain old radio. You set it to a frequency, then you push a button to talk. When you push the button a circuit completes that lets electricity flow through some components (used to be the mic, but now it's gone through changes at times, but it doesn't matter). Next the sound of your voice is encoded and applied over a carrier signal. Because that carrier signal can't be sent 100% of the time there was/is a bit of distortion at the start and end. In some radios they use a beep or click to help "establish" the carrier signal. Remember that the simplest radios just applied your voices wave form over that of the carrier signals.
Now, on the the receiving end, the same thing happens in reverse. The receiver can actually listen to the carrier signal the entire time, but there is a tiny delay as it starts to notice modulation of that signal, and starts "decoding it". Again remember the simple radio has your voice as a modulation of the carrier wave. These days there is a lot of logic on this end to filter out noise, but even if there wasn't it would still take a tiny amount of time to "see" that the carrier wave changed.
So you have several points of distortion and delay at the start and end of a message;

User pressing the button
The mic circuits "turning on"
The start of signal modulation
The start of signal demodulation
The Receiving end starting to "play back" the signal.

Add to that all kinds of distortion and interference, and the fact that as people we have a tendency to think along the lines of "push button -> talk" so fast that we often start "talking" before we are actually transmitting, and you can get some pretty messed up messages.
To combat that there are a few common things that are done.

Using longer words
Limiting vocabulary to common words
A set of hand shake phrases that ensure that both sides are getting the same thing.

For example (not from anything in particular):

You want pizza
  ooo want pizza
  ooo ..aunt... pee..ah

While a bit odd, all three could be understood if you're having a conversation about dinner.

Yes
  ess
  sss
  ye..

Is harder to understand than

Affirm
  ..Firm.
  Affir..
  Ah.ff.

Specially when you are asking a yes or no question.

No
  oh
  n...
  ...  (this is actually pretty common as yes and no are fast words to say)

So if you say into you radio "Do you want Pizza" and you get back: "...", your SOL. If you get back "oh", is that "oh I don't know" or the end of no? If you get back "Neg.." or "N....itive" or "Negiti.." You're still in good shape ( you have your answer).
There are many things radio operators are taught to do to make sure they can understand one another in less than perfect conditions. Using "longer" words is one, using distinct words is another, and using scripted responses and questions is a third.  It's also important to remember that rarely is the radio a "primary job" it's almost always a  "secondary job". The pilot needs to communicate, but communication can't be so cumbersome that it gets in the way of actually flying. So whatever system is in place to cover the distortion and what-not has to be easy, and widely understood.
Last example:
If you had two people with training, and they were taught that the question: "Do you want pizza?" could only EVER be answered with "... Yes ..." or "... No ..." then you could use yes or no, they sound different. But that means that the operator answering would have to press the button, count in their head to three, say YES, then count in their head to three, finally releasing the button. However if that operator was distracted, and didn't wait, or if the operator was out sick and the new guy didn't know the protocol, or there was a large network of people asking the question all with slightly different protocols, now "...Yes..." doesn't work as well.

What if you get "...itive"?

That's why a lot of systems use something other then Affirmative. Like just Affirm or 10-4 or Roger or such. Different systems different rules, but that's the basic problem that is trying to be addressed.

This good answer would be better if it used the actual "Affirm" from the question rather than "Affirmative", which is not recommended.

@GreenAsJade -"Affirmative" not recommended?  What guidelines say this, and do you happen to know of any US-based guidelines that say this?  (May be could be a new question-- )

Affirm and Negative are different, Affirmative and Negative sound the same at the end so getting back a ".....itive" would be less than ideal.

Because it increases the number of syllables being spoken thus increasing the likelihood of correct communication.


text:
How did NASA Langley end up with the first 737?
This answer shows N515NA, CN/MSN: 19437 as an early 737, and mentions that it may be the first one.
Was this a special design built for NASA, or perhaps a prototype that nobody wanted for commercial use?

NASA has lots of cool aircraft. They get them sometimes when they get to the end of their life/retired, sometimes they are custom built trainers, and sometimes they are used to test research projects. You can find the full history of that particular 737 here

NASA’s Boeing 737-100 Transport Systems Research Vehicle was the
  prototype 737, acquired by the Langley Research Center in 1974 to
  conduct research into advanced transport aircraft technologies.
...
The Boeing
  737 was Langley's number one choice, however,
  since it had a slightly wider fuselage and an
  advanced, high-lift flap system. Money however, was extremely tight. The
  market value of a used 737 in 1972 was about $3.5 million, but the
  Boeing Company had one particular 737 that its sales people said they
  might be willing to sell for substantially less."
...
Boeing had designated the prototype as PA-099: PA for Lufthansa, and
  099 as the last one in a block of 100 aircraft numbers Boeing had
  reserved for the airline. The prototype was never sold, however,
  because it was only certified for experimental use. With all the
  holes, wiring and other modifications that were made to the airplane
  for certification tests, bringing it up to the standards of a
  commercial transport airplane would have been too expensive. Boeing
  used the airplane for a few additional flight tests and then simply
  set it aside. '

In short, it was cheap, couldn't be used for commercial flight, and just what NASA needed. Chapter 2 in the above linked document covers the history in more depth and explains more of the nuances of the deal. To keep from copying the whole text I'll end it here.

This will make for some very enjoyable reading; thank you for such a thorough answer!

Ch. 2 pg. 11, or pg. 22 in the linked document.

Other interesting characteristics about this 737: it ending up costing NASA "only" $2.2 million, and it also included all of the technology that Boeing had created during its work on the USA's cancelled SST (supersonic transport) aircraft.

The design was originally built for the military and Langley air-force base as Dave mentioned.  It was then modified and given to NASA as the requested vehicle they needed.  The ease of transfer was primarily due to NASA and Langley have been deeply connected, even since NASA was first formed.  I cannot reveal all the details, but here is an example of someone who was connected to both Langley and the Apollo 11 astronauts: https://www.findagrave.com/memorial/138018057/howard-mac-lane
There were many Langley engineers and staff that worked on expediting approval and modifying the 737 for NASA to use.


text:
How did aircraft flying in formation use flares to communicate with each other?
The image shown in the question Which aircraft had such a luxurious-looking navigator's station? (also below) shows a flare gun with several flares.
A comment below the question says:

On the bonus question: flares were often used for communication between planes, sometime even when all planes in the formation had radio (to the point that new flare systems had to be designed for high altitude pressurized bombers at the end of WWII). Given the number of cartridges right under the flare gun, I think it is indeed for communication and not just for distress signaling, so you would probably want it readily available.

How common was it for this to be used, and how effective was it, especially during the day? When would it be used, and what would the flare indicate or communicate?
cropped and sharpened from https://i.sstatic.net/K0cO2.jpg used in here.
 Source.

I can't find a good source to back it up at the moment, but I'm pretty sure the Ka-50 has a signal flare system which can deploy color-coded signal flares. Also not sure if it is still present on the Ka-52. I'll try to develop this into an answer later.

German Me 109 fighters had a flare pistol mounted below the lower right windshield pointing, forward about 45 degrees, for signaling each other when radios didn't work or couldn't be used.

Navy craft around the WWII era definitely used flares for signalling, including for IFF purposes when radio communication was either impractical or being deliberately avoided (espionage and location-finding being the major reasons not to use radio or wireless telegraphy).

Author of the comment quoted: Sorry, I'm far from as knowledgeable on this subject than my comment could imply :) hence why I only made it a comment. The information I had was from this Forgotten Weapon  video about a pressurized plane's flare system, and what could be deduced from it.

@Luris welcome to Stack Exchange! There's nothing to say sorry about, the video is a great explanation and you can cite it as a source for your first SE answer. You can add both the Forgotten Weapons page and the YouTube as links, turn on Close Captions and write down one or two points from the narration, and add a screen shot like this one https://i.sstatic.net/jvS5b.jpg and you've got your first SE answer!

@Luris For some types of questions, multiple answers will get posted, and this will likely be that type of question.

This break down of a B24 Missions seems to outline the usage of flare on a mission well:

Assembly
After takeoff, a pilot usually kept on a straight course for about two
minutes, in part because the B-24 was not very maneuverable until it
had gained speed and altitude. The pilot then climbed at a
predetermined rate (about 300 feet per minute at 150 mph Indicated Air
Speed) to the assembly area assigned to the 392nd. A ship, usually
41-23689, Minerva, orbited a radio beacon at the prescribed altitude and fired designated colored flares to signal 392nd BG a/c. The
specified assembly altitude was based on cloud conditions. Clear skies
meant assembly could be at 5,000 to 10,000 feet. Often, though, pilots
had to climb to 20,000 feet or higher to get above the clouds, relying
on instruments to maintain headings, speeds and timed legs.

When on the actual mission...

Mission Routes
Routes were scheduled to avoid major flak areas as much as possible
and to mislead enemy fighters about the intended target. Each route,
then, included several course changes until the Initial Point (IP) was
reached. The IP was usually an unmistakable landmark, both visually
and on radar. At the IP, the lead plane alerted the formation to turn
toward the target by signal flares or by opening its bomb bay doors.
All other planes promptly opened their own bomb bays and made the turn
while simultaneously aligning in trail. On the bomb run, Groups were
usually two to five miles apart.

Then on the way home:

Wendling
By this time, the formation was down to a few hundred feet. While in the landing pattern circuit, the engineer confirmed the
wheels were down and locked. Planes with wounded aboard or severe
battle damage fired two red flares and landed first.

A few sources cite the M8 Flare gun being the one that was likely used during WWII. There is a discussion that covers some of the colors and cartridges here.

This book which talks about flare usage quite a bit, discusses a lot of the ground <-> air communication done with flares:

The increasing amount of airfield bombardment led to the establishment
of false aerodromes. These false fields gave the appearance of active
aerodromes by day and night in the hope that enemy bombers would be
fooled into releasing their bomb loads a mile or two from the real
airfields. At night, active fields remained concealed in darkness
until an airplane was properly identified through flare signals.

It goes on to say:

Signaling devices were necessary for communications with the ground.
The flare gun provided the most basic means of signaling. The Allies
used the Chobert, more commonly known as the Very pistol. British and
American night squadrons used three different colored Very cartridges,
red, white, and green. Each cartridge had a different milling along
its metal base flange so that aviators could quickly feel for the
correct shell in the dark.

Some flares were also used for ground illumination

Illuminating flares were developed for target acquisition and landing
assistance. One of the most important was the Holt wingtip landing
flare. Useful in an emergency or under inadequate field lighting
conditions, the Holt flare was ignited electrically (by dry cell
battery) from a push button in the cockpit. Typically the flare would
burn for a maximum of two minutes at up to 20,000 candlepower.

Thanks for the thorough answer, again! I'm pondering "orbited a radio beacon at the prescribed altitude". I'm guessing that orbited means it flew in a tight circle, but really curious what beaconing at a prescribed altitude meant in the block quote; if beacon direction-finding was sensitive enough to report an altitude difference (vertical angle) as well as a bearing. Do you think this warrants a separate question?

@uhoh orbiting a radio beacon is likely akin to if not the same as what we now call a holding pattern. Depending on what you want to know about holding a new question is likely warranted.

it's the altitude part I'm interested in, if the beacon was at a "prescribed altitude" in order to provide altitude information as well as bearing information.

@uhoh beacons do not provide altitude information, altimeters do. If you are told to hold on the XX beacon at 3000 you get the 3000 information from the altimeter in your aircraft and the distance/bearing information from the beacon. Typically those beacons are VOR's, VORTACs, TACANs or a GPS point but ATC can assign various types of holds around many things.

This makes so much more sense than what was going on in my head! I was thinking "radio silence, so open the canopy and fire a flare to indicate turn right", then "won't that flare be pretty visible to troops on the ground?".


text:
What is "scintillation" and are "qualified pilots" aware of it?
This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example in Nature's Air force had early warning of pulsars

Wikipedia's Crab Pulsar includes this passage:

Jocelyn Bell Burnell, who co-discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.

Question: What might "scintillation" be in this context, and are "qualified pilots" generally aware of it?

"Scintillation" is the flickering of starlight due to the turbulence in the Earth's atmosphere through which the light passes. It is also known as stars "twinkling."
The current version of the PHAK discusses a number of nighttime optical illusions, but not scintillation. It does discuss, however, autokinesis, which is a less well-known but similar illusion. I don't think it would be outrageous for a pilot who knows about scintillation to connect the two. After all, a pilot can discern the difference between a ground-based light source and a star because the star will scintillate and the ground-based light source will not. Maybe the PHAK should include it, given its interest in identifying false horizons created by lines of ground lights.
Someone knowledgable who observed the visual flicker of the Crab Pulsar would be able to easily tell that it wasn't scintillating because scintillation is random, whereas pulsar flickers are more precisely timed than atomic clocks.

Thanks for the speedy answer! I've now referenced this here.

Ground-based lights can flicker/twinkle too due to smog, fog, etc.

It would have been a well known phenomenon in the 1950's because star based navigation was very common, even for pilots, and "competent" pilots would have been trained in that regard.

I wonder if when Jane Taylor wrote the lullaby around 1806 she originally had it "Scintillate, scintillate little star..." then said, "Nah, that won't work!  Too many syllables!", tore it up and started over.

@StephenS: Or even if they're a long ways away, especially if you're flying in clear desert air fairly early at night, where there's a lot of differential heating of the ground, and air currents &c.  Indeed, you can get "twinkle" mirage effects in the daytime.


text:
Why does Google's Wing drone have dimples?

The question What operational aspects of Alphabet's Wing drone delivery service will be the same as that of an airline? includes a cropped photo of a google drone from FAA Certifies Google's Wing Drone Delivery Company To Operate As An Airline.
It is a winged aircraft with two long rows of vertical electric motors and propellors, and two more forward pointing motors for thrust, one on each wing.
The nose of the spacecraft is large and hemispherical and appears to be covered in small hemispherical dimples.
Question: Why the dimples?

Images below have been cropped, zoomed and substantially sharpened to enhance the visibility of the dimples.
Google's Wing Drone

Customers who took part in Wing's drone delivery test program in Virginia approach their package after it was dropped on their lawn. Credit: Wing Source

I've included the commercial-aviation tag because the craft is for commerce and this answer explains that though the company is not an airline, it is still considered a "air carrier".

Like a giant golf ball ?

@blacksmith37 it's hard to be sure from this photo, but it looks to me that these are probably "outies" rather than the "innies" found on golf balls, but I'm not sure how much of a difference that makes.

These are not actually dimples but shallow bulges. I found a higher-res image online and checked it out. You have to expand the image to full-size and look closely; the angle of sunlight and shadow gives them away:

Similarly, this side view shows that the bumps continue down the side:

The drone is not very large, less than 2 m (6 ft) long. They are not large enough to have significant aerodynamic effect at the speeds the drone flies. Lots of much faster planes have rows of rivet heads which stand out more than these do. They are about the size, shape and spacing one might expect from internal fixings holding a light supporting framework together, maybe there are pop-rivets under there. Another possibility is anchor points for internal equipment or wiring.
To be honest I am disappointed. Dimples are used on golf balls to stabilise flight and have in the past been studied as a way to reduce drag on aircraft. I had hoped at first that work might have been brought back to life. Then again, some cetaceans (whales etc) do have knobbles on their fins, we think to control the boundary layer and reduce drag, but these are just too small and shallow and not organised in the expected way for that.

I can't convince you that they are aerodynamic anti-dimples? :-) This certainly sounds like it's got a good chance of being the right answer, thanks!

They are just too small and shallow for the scale of the aircraft. Some cetaceans (whales etc) do have knobbles (or "anti-dimples" as you call them), we think to control the boundary layer and reduce drag, but these are just too small and shallow. Moreover, lots of planes have rows of rivet heads which stand out more than these do. I just updated my answer accordingly.

Excellent! I'm waiting for a picture of a real whale here in Aviation SE, so far I've only seen artificial ones (okay those aren't even artificial whales)

The humpback whale is one. See for example https://commons.wikimedia.org/wiki/File:Humpback_Whale_underwater_shot.jpg I should note there are other theories as to what the knobbles are for.

Since you found a higher-res image, would you be so kind as to [edit] your post to embed the image (if allowed by the hosts copyright terms) and include source info or at least include the link so others may see it.

Don't know about embedding, but I can post a link. It is so long that I will have to post it in a separate comment. Perhaps someone more skilled can embed it?

https://browse.startpage.com/do/show_picture.pl?l=english&rais=1&oiu=https%3A%2F%2Fo.aolcdn.com%2Fimages%2Fdims%3Fquality%3D85%26image_uri%3Dhttps%253A%252F%252Fo.aolcdn.com%252Fimages%252Fdims%253Fresize%253D2000%25252C2000%25252Cshrink%2526image_uri%253Dhttps%25253A%25252F%25252Fs.yimg.com%25252Fos%25252Fcreatr-uploaded-images%25252F2019-04%25252F2a27cf60-5ac5-11e9-9cb4-688fb32557c4%2526client%253Da1acac3e1b3290917d92%2526signature%253D8dd9e3294ab937bd47725afc11318241d6b6cf11%26client%3Damp-blogside-v2%26signature%3Db1245f4b6c8511bec6a4b2a9cf6c7f29f2bbbbca&sp=0c51fec0940e10ecfeb3e29adc56a65a


text:
Why this inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed
The pterostigma of insect wings an inertial regulator of wing pitch is linked in this answer to Why do dragonflies have these special little spots on their wings? (open access copy here)
The Summary of the paper includes the following points. I've highlighted some in bold.
Question: Is it possible to explain in simpler terms what "Inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed" means, and why these small weights do it?

The pterostigma of insect wings usually is a pigmented spot close to the leading edge far out on the wing, having a greater mass than an equally large wing piece in adjacent wing regions.

In several dragonfly (Odonata) species the position of the spanwise torsion axis of the wings, the mass distribution of the wings, and the position of the chordwise centre of mass in chordwise wing strips were determined.

In the dragonflies investigated, the torsion axis of the wing lies ahead of the chordwise centre of mass of the wing except at the pterostigma (Fig. 1).

A wing having its mass axis behind its torsion axis is very susceptible to self-excited coupled flapping and feathering vibrations, making gliding flight above a critical speed impossible. Due to unfavourable, inertial, wing pitching tendencies, a still lower speed limit is set to active flight.

Due to its mass contribution and favourable location, the pterostigma tends to raise these speed limits by causing favourable, inertial, pitching moments during the acceleration phases of wing flapping.

The favourable pitching moment of the pterostigma is proportional to the distance from the wing base to the pterostigma, and to the distance of the pterostigma ahead of the wing's spanwise torsion axis. The pterostigma usually has an optimal position at the leading edge of the wing near the wing tip, just where the wing curves backwards. Further optimization of pterostigma mass localization has been obtained in different ways in various insects, involving both pterostigma position (Fig. 4) and form (Fig. 5a).

The function of the pterostigma of raising the critical gliding speed, at which self-excited vibrations set in, was demonstrated in dragonflies. Although contributing only 0.1 % (one pterostigma) of the total dragonfly weight, it raised the critical speed by 10–25% in one species.

The pterostigma is common among the insect orders Odonata, Neuroptera, Psocoptera, Hemiptera, and Hymenoptera. By passive, inertial, pitch angle control, the pterostigma probably makes the wing beat more efficient in slow and hovering flight of small insects, while its raising of the critical flight speeds probably is of more importance to larger insects. The ability of active pitch angle control in many insects does not detract from the value of the pterostigma, since it contributes passively, without power expenditure, towards an efficient wing stroke.

Figures from the linked paper (click for full size):

Images from the linked question, click for full size:

I don't think this is on-topic for Av.SE, even though this may be the most likely place to find somebody who can answer it. The Help Center specifies (bold added): "Aerodynamics (related to aircraft)" so I think this is out-of-scope.

I disagree with the close votes, this is an aeroelasticity question that can be answered within the scope of this site. In particular, the asker seems to need an explanation of why a center of mass located in front of the elastic center of the wing section will produce a wing not susceptible to torsional divergence at high speeds. If Peter doesn't beat me to it, I will post an answer tonight.

Ok, not tonight, I need to trim the wall of text the draft turned into to make it approachable.

@AEheresupportsMonica thank you, I appreciate the help! btw it may be possible to post a partial answer indicating that it will be fleshed out the next day. I sometime do this when a question is in dire peril of having answer posting blocked when it arguably shouldn't be.

@uhoh I posted the introductory paragraphs; hope this helps stave off closure.

Short answer:
Adding a mass ahead of the elastic axis of the wing tends to increase the critical flutter speed of the wing, thus allowing a larger flight envelope. Above this critical speed the wing would experience vibrations of increasing amplitude that could lead to its destruction (or to a limit-cycle flutter mode, which is also bad but less so than rapid unplanned disassembly).
Flutter is a destructive aeroelastic phenomenon that can be described (in a simplified way) as a combination of two natural vibration modes of a wing. These modes are torsion around a spanwise axis and bending with respect to the root. Each mode will have a natural frequency, and the flutter speed will have a minimum (not guaranteed to be a global one, btw) when both of these frequencies are the same, because then they will reinforce one another.
The distance between the center of mass and the elastic axis of the wing is very important for the torsion response of the wing, simply because the wing will twist around this elastic axis, and a center of mass far away from it will give high inertial moments.
By adding weight to the leading edge, the dynamic behavior of the wing is modified in a way that moves the critical flutter speed upwards, extending the safe flight envelope. This technique can be seen most often in helicopter blades, many of which have some trim or balance weight at the leading edge.
Long answer (math ahead):
WIP - The analytical treatment is quite long so I am trying to decide which results are actually worth typing into MathJax

This short answer is already useful

Ping me when you think you've reached a stopping point. I'm sure you can just cite the math and state the results or basic idea. The statement "Flutter is a destructive aeroelastic phenomenon" could be supported with a link to allow those interested to read further.

...but in the interim I'll click accept :-)

Another aerodynamics question, possibly up your alley? What are “secondary precessional forces”? Help understanding the aerodynamics behind the first successful returning boomerang flight in microgravity

for readers getting this far, this may also be of interest: Using dragonfly wings to study the relationship between corrugated wing structure and vortex motions


text:
What are these engineers doing sitting on a large format drawing of B-47s aircraft?
This answer about solid-jet-assisted takeoff links to the page B-47 Jet-Assisted Take Off (JATO). An image there took me to a collection of historical aviation images, apparently from a LIFE Magazine archive.
Browsing there led me to the image below, of what looks like several aviation engineers sitting on a very large format drawing of a B-47 aircraft and its major components.
A reverse image search leads mostly to sites written in Russian, which I can't read.
Does anyone recognize what's actually happening here? It's not scene one would normally see these days.

source: http://images.google.com/hosted/life/2ce91e390933d837.html

B-47 Stratojet Bomber, Date taken: September 9, 1950 Photographer: Howard Sochurek

It's still a valuable exercise to work with scale models to plan out large processes like aircraft production. 3D printing has only made that even easier.

Thanks man for the picture , it will be on my wall :)

Online translators are actually pretty decent the next time you are stuck like this.

@Infiltrator depending on the particular language, your milage may vary, and without a native speaker to review the on-line translation, how can one identify the  inevitable errors and mistranslations?

@uhoh: It is not a solution, of course.  I just mean that it can be the first tool for which you reach.

@AliErdem Dostum I think it is a nice resim and it is good to have this aviation tutkusu too.

@F.Bek is it your first time running into someone from your country in internet :) why don't we be friends btw, we can share some beer or tea and talk about Kelly Johnson

They appear to be squatting or leaning over, not sitting.

@jpmc26  - The guy at the top left (white shirt=supervisor) seems to be grasping his temple and saying "Oh, crap... they did it just like I told them to - I'm going to loose my job!"

@jwzumwalt I was going to suggest it's a variant of Twister played only by aerospace engineers ...

@AliErdem I would love to talk about aviation and beer sounds amazing. I have Linkedin profile linked to my stackexchange account. Lets connect ! Then I will delete these funny comments.

related in an aesthetic way: https://retrocomputing.stackexchange.com/a/11145/7118

As commented by Anilv, they are examining a factory production layout/plan. They most likely are attempting to resolve a production or supply problem, though as Anilv suggests, they may also be planning the factory layout.
Listed below is an example of the (edit) B-29 Flying Fortress Factory Production Layout used by Boeing in WWII. Note the arrows which show the production procession and parts/sub-assembly entry and exit.

Source - Boeing

Yes, I can immediately understand now, this makes a lot of sense, thank you!

Those look like B-29's.

I think Boeing knows what their own airplanes look like, the picture was from their web site? They probably were not interested in a scientifically accurate silhouette.

They are indeed B-29's, look at the trailing edge of the wings, the inner engine nacelles have a fillet that extends beyond the trailing edge of the wing on the B-29, the B-17 does not. The wings are narrower on the B-29, too. And even the manufacturer can make a mistake and mislabel the image.

Good answer, but as to what they're doing (planning or troubleshooting something), we should realize that they may simply be posing for a good photo. :)

@Davidw - I think artistic license was used. I admit the art department used B-29 for the B-17 but the nose and cowl of a B-29 are longer. It looks like they  took a B-29 silhouette and scaled it for a B-17. If you look at the top right compared to the bottom right, the tip profile is significantly different in width. The trailing edge wing of a B-29 is nearly straight horizontally while the B-17 is noticeably tapered; the silhouette is half way in-between. In war, you grab what ever will get through the day and run with it. It looks like someone took their scissors and said "good enough".

@TypeIA - I thought they were from New York and were pitching pennies. Shows what I know...

Just to confirm, one of the sites you mentioned says:

Планирование производства бомбардировщиков B–47 на заводе ВВС США №6.
  Завод ВВС США №6, был построен в 1942–1943 годах в небольшом городке Мариетта, штат Джорджия, для Bell corporation, и предназначался для выпуска бомбардировщиков B–29.
Завод до сих пор остается одним из крупнейших зданий в мире, его площадь под одной крышей составляет 390200 м2.
  После войны завод был закрыт, но в 50-х годах открыт вновь, вначале для ремонта и модернизации бомбардировщиков B–50, а затем для производства B–47 силами компании Lockheed Martin.
Завод работает и в настоящее время, на нем производится ремонт и обслуживание самолетов ВВС США, в том числе Lockheed/Boeing F-22 Raptor.

That translates to (emphasis mine):

Planning the production of B-47 bombers at the US Air Force plant No. 6.
  US Air Force No. 6, was built in 1942-1943 in the small town of Marietta, Georgia, for Bell corporation, and was intended for the production of B-29 bombers.
  The plant still remains one of the largest buildings in the world, its area under one roof is 390,200 m².
After the war, the plant was closed, but in the 1950s it was reopened, first to repair and modernize the B-50 bombers, and then to manufacture the B-47 by Lockheed Martin.
The plant is currently in operation and repairing and servicing the US Air Force aircraft, including Lockheed / Boeing F-22 Raptor.

Thank you for this! It seems to be quite informative.

@uhoh you can use Google Translate on web pages in languages you can't read, it's not perfect but it gives you an idea of what it's about.


text:
What is this transport aircraft, and why does it sometimes cary an air data boom when the Soviet Buran Space Shuttle is on top of it?
This comment in chat points to a "google search of the day" which was for Buran the Soviet version of the Space Shuttle. Looking there I saw images of a large transport aircraft with the Buran shuttle on top. What caught my eye were some photos of  the transport aircraft with what looks like a large, orange air data boom at the end.
My understanding from Quora answers is that these are used for supersonic flight, and I wouldn't expect this shuttle to be transported supersonically.
Question: What is this transport aircraft, and why does it sometimes cary an air data boom when the Buran shuttle is on top of it?
According to this blog it is an Antonov AN-225 but I don't think that is a supersonic aircraft.

above: From thelivingmoon.com. Click for full size views.
below: I believe this is Buran itself, According to @Hobbes' correction/comment, this is the "OK-GLI: a Buran analog (shape is correct, systems are not identical to the orbital vehicle) with 4 jet engines that was used for flight testing in the atmosphere", also with an air data boom. I've kept this here because it's actually pretty cool. From pinterest.

Another question would be why the aircraft seems to have only one wing?  The right one should be visible at that angle, and in front of the tower structure...

It is indeed an An-225 (the first and only one built). A spike like this does not mean this aircraft is supersonic. It can also be to put sensors as far away from the disturbe airflow (du to the big flying machine carrying it) as possible. I don't know if it is the case here, but some prototype tow such sensors to calibrate the onboard sensors.

I believe the air data sensor boom is indeed to get the sensors into undisturbed air in front of the craft, possibly to check whether its own sensors give correct readings even with the Buran on top modifying the air flow around the Antonov. Its right wing is visible behind the tower structure (different distances to left and right structures).

@jamesqf I can clearly see the right wing in the left part of the pictures

@ManuH please post that as an answer

@CptReynolds ibidem

@Federico I'll probably ask for an example or reference showing that aircraft sometimes use these circa mach 0.5, otherwise it's just speculation.

@jamesqf the right wing is behind the green structure.

@Federico It’s still speculation on my part, unfortunately. I don’t have meaningful knowledge or sources on Buran ops and transportation...

This sub-sonic aircraft has a smaller boom, and may be Russian, but I don't think it's a suitable example. https://i.sstatic.net/Mb998.jpg

The last photo shows the OK-GLI: a Buran analog (shape is correct, systems are not identical to the orbital vehicle) with 4 jet engines that was used for flight testing in the atmosphere.

@Hobbes aha! I'd included it quickly without looking carefully, then realized it was shuttle-shaped rather than plane-shaped so made an excuse. Now I know why, those jet engines! I'll re-edit again, thanks!

@Femaref: I don't see how that can be possible.  The green structure appears to be behind the main landing gear, yet the leading edge of the wing is ahead of the gear at its root - where the person in the red shirt is standing.

@jamesqf It's quite a boggling image. There's some foreshortening since the photographer is fairly close to the front of the boom, but ya, they may have had to remove a wing (or part of it) because of the crane. However if you look at the first grayscale image (click to open full size) I think I can see the other wing. Again, it's the foreshortening that makes it look so weird! Looking to the extreme left of the top image, yep, there's a wing there, emerging from behind the green structure.

https://i.imgur.com/wxsF7Ly.jpg?1 I've marked out one of the engines in red as well as the wing line in black. It's a very weird perspective. The structure is also quite thin, much thinner than it appears to be. some weird optic trickery going on.

@Femaref Great! I think a wide angle lens was used, which can add some non-intuitive distortion. The Buran shuttle doesn't even seem to be centered on the AN-225 (though maybe that's just me). Alternative, conspiracy theory: Photoshop?

The only aircraft that ever had a shuttle on top of them is NASA's modified Boeing 747 and Russia's Myasishchev and the Antonov 225. All of them were subsonic.
The one in the picture is the high wing 6 engine Antonov 225.
The air data boom is likely to gather data for test flights for the shuttle. Subsonic craft will affect the air in front of them (that's why you can hear them coming) so putting the sensor on a boom will help put the sensors in clean air.

@uhoh not really, you want an as clean as possible reading on the sensors, subsonic craft will affect the air in front of them (that's why you can hear them coming) so putting the sensor on a boom will help.

Thanks! So if this is a one-of-a-kind aircraft and doesn't have much history flying like this, then it may be more necessary to add such an instrument since the effect of the shuttle is unknown. For the US Space shuttle, the carrier is (probably) a NASA 747 and there is probably much more experience. https://youtu.be/MhwSbeiRADA See also https://en.wikipedia.org/wiki/Shuttle_Carrier_Aircraft#Design_and_development and also this answer.

During flight testing, an aircraft's onboard instruments and sensors must be calibrated and validated. Pitot-static systems located on the fuselage are affected by the air flow around the aircraft. Some other measurement is needed to establish the relationship between actual atmospheric conditions and what the aircraft sensors measure.
One method is the boom extending from the nose. This takes measurements far enough in front of the aircraft that the air is undisturbed by the aircraft itself. Supersonic aircraft must use the boom method because the air flow behind the aircraft has been affected by the shockwaves created by the nose and other aircraft features. Especially in larger aircraft this is an expensive installation, and would interfere with the weather radar in the nose.
Another method of measuring actual conditions is a trailing cone extended behind the aircraft. This requires modification of the aircraft structure and is susceptible to damage.
The An-225 was built specifically to carry the Buran, so it makes sense that they would test it with the Buran on top. It would also create an especially large wake that might make a trailing cone difficult.

Supplementary to @ratchetfreak's accepted answer I'd like to include an image that demonstrates air data booms are used on sub-sonic aircraft as well.
From @fooot's comment linking to This Day in Aviation for 30 June 1968, here are photos of a prototype Lockheed C-5A Galaxy and it's first flight. This amplifies the point that the air data boom is important to establish better measurements for new aircraft or those with unusual configurations.

above: The prototype Lockheed C-5A Galaxy, 66-8303, at Marietta, Georgia, 30 June 1968.  (Bettmann/CORBIS) From here.
below: Lockheed C-5A Galaxy 66-8303 during its first flight. (Code One Magazine). From here. Click for full size.

I don't understand the downvote.

It is indeed an An-225 (the first and only one built). A spike like this does not mean this aircraft is supersonic (as highlight by this question). It can also be to put sensors as far away from the disturbe airflow (du to the big flying machine carrying it) as possible. I don't know if it is the case here, but some prototype tow such sensors to calibrate the onboard sensors as explained in this video (french).

Have you ever seen a sub-sonic aircraft with a boom? Both answers say it's possible, but so far no other examples have emerged. So far I can't get the video to play here either.

@uhoh the C-5 is another example that used a boom in flight test.

@fooot excellent! (Same color too!) It would be great to see one or both images as part of an answer.